The present invention relates to a high performance manganese zinc ferrite (Mnxe2x80x94Zn ferrite) with small core loss and high magnetic flux density, and in particular to a Mnxe2x80x94Zn ferrite suited to ferrite cores for transformers of power supply.
Ferrite cores for transformers to be used to an electric source have been demanded for low core loss and high saturation magnetic flux density going with nowadays miniaturization and high efficiency of electronic devices.
Accordingly, ferrite such as under mentioned has conventionally been proposed.
JP-A-60-132301 proposes a ferrite contains CaO and Nb2O5 in a basic composition comprising Fe2O3, MnO and ZnO, and further contains one of SiO2, V2O5, Al2O3, CoO, CuO and ZrO2 to reduce core loss. However, for realizing miniaturization and high efficiency of transformers, further reduction of the core loss is required, and no consideration has been taken at all for saturation magnetic flux density being as one of important requisite properties together with the core loss.
JP-A-7-297020 improves the core loss at 100xc2x0 C. by Sn and Ti in the ferrite. In general, it is known that when Sn or Ti is added to Mnxe2x80x94Zn ferrite, a temperature that the core loss indicates a minimum (xe2x80x9cminimum temperaturexe2x80x9d hereafter) is shifted to a low temperature. Accordingly, unless Fe or Zn is decreased in company with the contents of Sn or Ti, the temperature characteristic of the core loss is deviated. At this time, the core loss at high temperature increases and the saturation magnetic flux density decreases. In addition, as Sn and Ti are non-magnetic, the saturation magnetic flux density decreases.
JP-A-10-64715 contains a basic composition of Fe2O3, MnO, ZnO and NiO, and further contains one or two kinds or more of Ta2O5, ZrO2, Nb2O5, V2O5, TiO2 and HfO2 to improve the core loss and the saturation magnetic flux density. Although the high saturation magnetic flux density is provided at a high temperature range because of containing NiO, a magnetic anisotropy is assumed to be large since NiO content is as much as 0.5 to 4 mol % (0.3 to 2.5 wt %), and the core loss is scarcely improved.
Accordingly, it is an object of the invention to offer a high performance manganese zinc (Mnxe2x80x94Zn) ferrite of higher saturation magnetic flux density and low loss at core mounting temperature for transformers for satisfying such demands.
The object of the invention can be accomplished by the followings.
According to the present invention, Mnxe2x80x94Zn ferrite comprises a main component comprising iron oxide 52.5 to 54.0 mol % in terms of Fe2O3, zinc oxide 7.7 to 10.8 mol % in terms of ZnO, and the remaining being MnO, and sub-components of silicon oxide 60 to 140 ppm in terms of SiO2, calcium oxide 350 to 700 ppm in terms of CaO, and nickel oxide 4500 ppm or lower (not including 0) in terms of NiO.
Preferably, Mnxe2x80x94Zn ferrite as set forth the above may contain zinc oxide 9.1 to 10.8 mol % in terms of ZnO.
Preferably, Mnxe2x80x94Zn ferrite as set forth the above may contains nickel oxide less than 3000 ppm (not including 0) in terms of NiO.
Preferably, MnZn ferrite as set forth in the above may contain sub-components of niobium oxide 100 to 350 ppm in terms of Nb2O5 and zirconium oxide 350 ppm or lower (including 0) in terms of ZrO2 to follow an under formula of
400 (ppm)xe2x89xa6ZrO2 (ppm)+2*Nb2O5 (ppm)xe2x89xa6800 (ppm).
Preferably, it is included zirconium oxide 50 to 350 ppm in terms of ZrO2.
Preferably, Mnxe2x80x94Zn ferrite as set forth the above may contain phosphorous P less than 30 ppm for the main component.
Preferably, Mnxe2x80x94Zn ferrite as set forth the above may contain boron B less than 30 ppm for the main component.
Thereby, the under mentioned working effects are exhibited.
It is possible to provide a MnZn ferrite of very small core loss and high saturation magnetic flux density in a core for transformer to be used nearly at 100xc2x0 C. In addition, it is possible to select a composition of low core loss and high saturation magnetic flux density.
By containing ZnO 9.1 to 10.8 mol %, a temperature dependency of the core loss at higher temperature than 100xc2x0 C. is reduced, and it is easy to manufacture MnZn ferrite of smaller core loss than prior art ones.
Since nickel oxide is contained less than 3000 ppm in terms of NiO, a MnZn ferrite of smaller core loss may be obtained.
As niobium oxide 100 to 350 ppm in terms of Nb2O5 and zirconium oxide 350 ppm in terms of ZrO2 are contained in the range of 400 (ppm)xe2x89xa6ZrO2 (ppm)+2*Nb2O5 (ppm)xe2x89xa6800 (ppm), a MnZn ferrite of small core loss may be obtained.
Further, in the above Mnxe2x80x94Zn ferrite, since zirconium oxide 50 to 350 ppm in terms of ZrO2 is contained, a MnZn ferrite of still smaller core loss may be obtained.
Since phosphorous P is contained 30 ppm or lower for the main component, a Mnxe2x80x94Zn ferrite of small core loss is available.
Since boron B is contained 30 ppm or lower for the main component, a Mnxe2x80x94Zn ferrite of small core loss is also available.